Method for robotic handling using thermo-reversible dry adhesives

ABSTRACT

One embodiment includes an application of multilayer thermo-reversible dry adhesives in robotic handling of objects.

This application claims the benefit of U.S. Provisional Application No.60/925,418, filed Apr. 20, 2007.

FIELD OF THE INVENTION

The field to which the disclosure generally relates includes dryadhesives used in the robotic handling of objects.

BACKGROUND

Gecko feet pads, with nanohair structures on them, are examples of smartdry adhesives. The working principle of the Gecko adhesion is that thenanohair structure allows the foot pad to make maximum contact with acounter surface regardless of its roughness and chemical composition.This is accomplished by nanohairs that are relatively long andprotruding from the foot pad at an angle so that adjacent nanohairs cancontact the counter surface regardless of its topography. The maximumcontact further allows for accumulation of millions of small van derWaals (in the range of microNewtons) interactions between the Gecko footpad and the counter surface, leading to an overall adhesion force(pull-off force) of about 10 N/cm². When the detaching force is employedin a peel-off mode, however, the complete detachment is achievedgradually by overcoming small adhesion forces corresponding to verysmall areas. Thus, the adhesion is easily reversed. Overall, theattractiveness of the Gecko adhesion lies in the combination of adhesivestrength (10 N/cm²), reversibility, and the ability to adapt to avariety of surfaces in terms of both the surface roughness andcomposition. The above unique features of the Gecko adhesion hasstimulated scientific research efforts to produce synthetic smart dryadhesives that work using the same principle as the Gecko feet. Up tonow, the two best synthetic Gecko adhesives show maximum pull-off forceof 3 and 10 N/cm², respectively. Both adhesives suffer from severeadhesion loss after only one or two attaching/detaching cycles, as aresult of breakdown of the nano structures. Often this occurs whenadjacent elongated structures simulating the nano hairs of the Geckofoot pad bond to each other. In addition, synthetic Gecko adhesives areexpensive to produce and large-scale manufacturing is practically toodifficult.

SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION

One embodiment includes an application of multilayer thermo-reversibledry adhesives in robotic handling of objects.

Other exemplary embodiments of the invention will become apparent fromthe detailed description provided hereinafter. It should be understoodthat the detailed description and specific examples, while disclosingexemplary embodiments of the invention, are intended for purposes ofillustration only and are not intended to limit the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will become more fullyunderstood from the detailed description and the accompanying drawings,wherein:

FIG. 1A illustrates a method according to one embodiment.

FIG. 1B illustrates a method according to one embodiment.

FIG. 1C illustrates a method according to one embodiment.

FIG. 1D illustrates a method according to one embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description of the embodiment(s) is merely exemplary innature and is in no way intended to limit the invention, itsapplication, or uses.

Referring to FIGS. 1A-1D, one embodiment of the invention includes arobot 10 having a thermo-reversible dry adhesive 12 on a portion of therobot, for example but not limited to on the tip of a robot arm 14. Inone embodiment, at least one of a heating or cooling wire may beprovided and embedded in the robot arm. In another embodiment, at leastone of a heating or cooling wire may be attached to thethermo-reversible dry adhesive. In various embodiments, thethermo-reversible dry adhesive may comprise a dry adhesive layer 16 anda shape memory polymer layer 18.

Still referring to FIGS. 1A-1D, one embodiment includes a method ofpicking up an object 20 using the robot 10 having the thermo-reversibledry adhesive 12 on a portion of the robot, for example the robot arm 14.Referring to FIG. 1A, the dry adhesive layer 16 may first be heated by abrief electrical current through the heating wire to a temperature abovethe glass transition temperature of the shape memory polymer. Then thedry adhesive layer on the robot may be pressed against the intendedobject 20 to make contact, as shown in FIG. 1B. The dry adhesive layermay then be cooled down either by natural cooling or using a coolingwire. This causes a strong adhesive bond to be formed between the dryadhesive layer and the object. In one embodiment, the pull-off force maybe approximately 40 N/cm² relative to glass, but the pull-off force mayvary depending upon the object. The strong adhesion between the objectand the dry adhesive layer allows the object to be moved by the roboticarm.

As shown in FIG. 1C, in one embodiment, the robot arm 14 may becontrolled to carry the object 20 to a target location 22. Then theobject 20 may be released at the target location by heating the dryadhesive layer again using electrical current through the heating wireto a temperature above the glass transition temperature of the shapememory polymer, as illustrated in FIG. 1D. In one embodiment, thedetachment of the object from the dry adhesive layer requires only arelatively small force, for example about 0.5 N/cm². In anotherembodiment, the detachment requires only a small force of about 0.3N/cm². In another embodiment, the detachment requires a force notgreater than 2 N/cm².

In another embodiment, a Peltier thermal electric device, which iscapable of both heating and cooling, may be utilized to heat and coolthe thermo-reversible dry adhesive. The Peltier device may include a PNjunction and may be constructed and arranged so that current flowingthrough the PN junction in one direction causes the device to heat oneside thereof and current flowing through the PN junction in the oppositedirection causes one side thereof to cool the device.

In one embodiment, the robot having a thermo-reversible dry adhesive onthe tip of the robot arm may be used to handle a wide variety of largeobjects. For example, the robot may be used to handle windshield glassin an automotive assembly plant. In one embodiment, the dry adhesive isheated and pressed against the surface of the windshield glass. Uponcooling, a strong adhesive bond is formed and the windshield glass maybe moved with the robot arm. Once the windshield glass is in place, thedry adhesive and robot arm may be detached from the glass by heating thedry adhesive.

In various embodiments, the dry adhesive layer 16 may be an epoxyelastomeric dry adhesive. In various embodiments, the shape memorypolymer layer 18 may be an epoxy shape memory polymer. In variousembodiments, the components of the dry adhesive or the components of theshape memory polymer may include a rigid epoxy and a flexible epoxy. Therange of possible crosslinking chemistries which may be used to achievea dry adhesive or shape memory polymer may include alpha,omega-diaminoalkanes, organic multi-carboxylic acid, anhydride, orcatalytic (as in imidazole type) crosslinking reactions. There are manydifferent ways to achieve the appropriate relationships between themolecular properties. For example, the dry adhesives or shape memorypolymers may include a rigid epoxy, an epoxy extender, and acrosslinking agent; or a rigid epoxy, a flexible crosslinking agent, anda flexible epoxy; or a rigid epoxy, a rigid crosslinking agent, and aflexible epoxy; or a rigid epoxy, a flexible epoxy, and a catalyticcuring agent; or a rigid epoxy, a crosslinking agent, and a diluent; ora flexible epoxy, a crosslinking agent, and a diluent; or a rigid epoxyand a flexible crosslinking agent; or a flexible epoxy and a catalyticcuring agent; or a flexible epoxy and a crosslinking agent; and whereinthe rigid epoxy is an aromatic epoxy having at least two epoxide groups,the flexible epoxy is an aliphatic epoxy having at least two epoxidegroups, the epoxy extender has one epoxide group, and the crosslinkingagent is one of a multi-amine, an organic multi-carboxylic acid, or ananhydride, and the diluent is a monoamine or a mono-carboxylic acid. Invarious embodiments, the catalytic curing agent (or catalytic cure)promotes epoxy-to-epoxy or epoxy-to-hydroxyl reactions. The catalyticcuring agent may include, but is not limited to, tertiary amines, aminesalts, boron trifluoride complexes, or amine borates. In one embodiment,the components of the dry adhesive may be present in an amountsufficient to provide, upon curing of the composition, a dry adhesivehaving a glass transition temperature (T_(g)) of −90° C. to 200° C. andhaving a pull-off strength of 1-200 N/cm² from a substrate. In anotherembodiment, the dry adhesive may have a glass transition temperature of−90° C. to 25° C. In one embodiment, the components of the shape memorypolymer composition may be present in an amount sufficient to provide,upon curing of the composition, an epoxy shape memory polymer having achange in storage modulus of 2 to 3 orders of magnitude before and afterits glass transition.

One embodiment of the invention includes a multilayer thermo-reversibledry adhesive having a first layer made from an aromatic diepoxide (rigidepoxy), an aliphatic diepoxy (flexible epoxy), and a diamine curingagent, and a second layer made from an aliphatic diepoxy and an amine.In one embodiment the multilayer thermo-reversible dry adhesive has acurved structure.

Numerous shape memory polymers may be utilized in various embodiments ofthe invention. For example, starting with a typical aromaticdiepoxy/diamine system with a T_(g) of about 90° C., the aromatic epoxycomponent is replaced systematically with an aliphatic diepoxy to yielda series of epoxy shape memory polymers with T_(g)'s ranging from 3° C.to 90° C. As such, a shape memory polymer may be tailored for use with adry adhesive as desired for a particular application operated withincertain temperature ranges.

Some embodiments refer to a multilayer epoxy dry adhesive. It should beunderstood that more than two layers may be utilized. For example, theremay be two or more layers of the shape memory polymer layer, which maybe in a side by side relationship or an overlying relationship.Likewise, there may be two or more dry adhesive layers in a side by siderelationship or an overlying relationship. As such, a device with customor tailored properties may be manufactured.

One embodiment of the invention includes a method of making a multilayerthermo-reversible dry adhesive comprising heating 3.6 g of EPON 826 (thediglycidyl ether of bisphenol A epoxy monomer) to about 75° C. andmixing the same with 2.16 g of neopentyl glycol diglycidyl ether (NGDE)and 2.3 g of Jeffamine D-230, which is the curing agent poly(propyleneglycol)bis(2-aminopropyl)ether. Jeffamine D-230 is a polyetheramine thatis difunctional, primary amine with an average molecular weight of about230. The primary amine groups are located on secondary carbons at theend of the aliphatic polyether chain. Jeffamine is available fromHuntsman.

The mixture was then poured into an aluminum pan and cured in an oven atabout 100° C. for 1.5 hours. Then a mixture of 2.6 g of NGDE and 1.15 gof an amine such as Jeffamine D-230 was poured into the aluminum pan ontop of the first cured epoxy layer and cured for 1.5 hours at 100° C. Ina third step, the oven temperature was raised to 130° C. for post-curingfor about one hour. At the end of the post-curing, the cured two-layerepoxy was demolded. A double layer epoxy was obtained with the firstlayer which had a thickness of about 2 mm and functioned as a shapememory polymer with a glass transition of about 45° C. and a secondlayer as a dry adhesive having a thickness of about 1 mm. The yieldeddouble layer epoxy structure had a slightly curved structure due to thethermal mismatch between the first and second layers. This curvature canalso be created by specifically designed molds to achieve the curvedstructure.

The above description of embodiments of the invention is merelyexemplary in nature and, thus, variations thereof are not to be regardedas a departure from the spirit and scope of the invention.

1. A product comprising a robot comprising a robot arm and athermo-reversible dry adhesive secured to the robot arm, wherein thethermo-reversible dry adhesive comprises a shape memory polymer layerand a dry adhesive layer underlying the shape memory polymer layer.
 2. Aproduct as set forth in claim 1 wherein the dry adhesive layercomprises: at least one of a rigid epoxy or a flexible epoxy; and atleast one of a crosslinking agent or a catalytic curing agent; whereinthe rigid epoxy is an aromatic epoxy having at least two epoxide groups,the flexible epoxy is an aliphatic epoxy having at least two epoxidegroups, and the crosslinking agent is one of a multi-amine, an organicmulti-carboxylic acid, or an anhydride.
 3. A product as set forth inclaim 1 wherein the shape memory polymer layer comprises: at least oneof a rigid epoxy or a flexible epoxy; and at least one of a crosslinkingagent or a catalytic curing agent; wherein the rigid epoxy is anaromatic epoxy having at least two epoxide groups, the flexible epoxy isan aliphatic epoxy having at least two epoxide groups, and thecrosslinking agent is one of a multi-amine, an organic multi-carboxylicacid, or an anhydride.
 4. A method of moving an object comprising:providing a robot having a robot arm and a thermo-reversible dryadhesive attached to the robot arm; heating the dry adhesive andpressing the adhesive against an object to make contact; cooling downthe adhesive so that a strong adhesive bond is formed; controlling therobot arm to carry the object to a target location; and releasing theobject comprising heating the dry adhesive again and using a force notgreater than 2 N/cm² to detach the robot arm and adhesive from theobject.
 5. A method as set forth in claim 4 wherein the adhesive bondhas a pull-off force greater than 10 N/cm².
 6. A method as set forth inclaim 4 comprising using a force not greater than 0.3 N/cm² to detachthe robot arm and adhesive from the object.
 7. A method as set forth inclaim 4 wherein the thermo-reversible dry adhesive comprises a shapememory polymer layer and a dry adhesive layer underlying the shapememory polymer layer.
 8. A method as set forth in claim 7 wherein thedry adhesive layer comprises: at least one of a rigid epoxy or aflexible epoxy; and at least one of a crosslinking agent or a catalyticcuring agent; wherein the rigid epoxy is an aromatic epoxy having atleast two epoxide groups, the flexible epoxy is an aliphatic epoxyhaving at least two epoxide groups, and the crosslinking agent is one ofa multi-amine, an organic multi-carboxylic acid, or an anhydride.
 9. Amethod as set forth in claim 7 wherein the shape memory polymer layercomprises: at least one of a rigid epoxy or a flexible epoxy; and atleast one of a crosslinking agent or a catalytic curing agent; whereinthe rigid epoxy is an aromatic epoxy having at least two epoxide groups,the flexible epoxy is an aliphatic epoxy having at least two epoxidegroups, and the crosslinking agent is one of a multi-amine, an organicmulti-carboxylic acid, or an anhydride.
 10. A method of handling anobject using a robot with a multilayer adhesive and separating theobject and the robot by thermally reversing the adhesion via heating.